This invention is generally concerned with methods and apparatus for protecting data in a computer during power failure conditions and more particularly for protecting current operating data in an electronic postage meter upon the occurrence of a power failure condition.
Numerous systems have been designed to preserve information stored in electronic memory units during power failures. Examples of systems of this type are shown in U.S. Pat. No. 3,676,717 for NON-VOLATILE FLIP-FLOP MEMORY CELL; U.S. Pat. No. 3,859,638 for a NON-VOLATILE MEMORY UNIT WITH AUTOMATIC STANDBY POWER SUPPLY; and U.S. Pat. No. 4,049,951 for DATA DETECTION APPARATUS. Such systems generally involve sensing the power failure and taking measures to insure that data is not lost, such as by employing an auxiliary source of power for providing standby power when the primary power supply experiences a failure condition, and loading the data into a non-volatile memory prior to loss of standby power. Other U.S. patents which show systems to protect stored information are U.S. Pat. No. 3,801,963 for METHOD AND APPARATUS FOR TRANSFERRING DATA FROM A VOLATILE DATA STORE UPON THE OCCURRENCE OF A POWER FAILURE IN A COMPUTER; U.S. Pat. No. 3,810,116, for VOLATILE MEMORY PROTECTION; U.S. Pat. No. 3,959,778 for APPARATUS FOR TRANSFERRING DATA FROM A VOLATILE MAIN MEMORY TO A STORE UNIT UPON THE OCCURRENCE OF AN ELECTRICAL SUPPLY FAILURE IN A DATA PROCESSING SYSTEM and U.S. Pat. No. 3,980,935 for VOLATILE MEMORY SUPPORT SYSTEM.
An early, typical, system for protecting data in the event of a power failure condition in an electronic postage meter is shown in U.S. Pat. No. 3,978,457 for MICROCOMPUTERIZED ELECTRONIC POSTAGE METER SYSTEM. In this system, when the supply voltage drops below a threshold level, a shut down signal is generated which causes the postage meter's microcomputer to initiate a shut down routine. As part cf the shut down routine, the contents of a working, random access, memory are transferred to a non-volatile memory. Power is made available during the time period needed to detect the shut down signal and to transfer the register contents from the working memory to the non-volatile memory by providing the power supply with at least one large filter capacitor which discharges during a time interval of sufficient length to maintain a working voltage range during the time period.
Examples of more recent systems for protecting stored data in electronic postage meters upon the occurrence of power failure conditions may be found in U.S. Pat. No. 4,253,015 for an ELECTRONIC POSTAGE METER HAVING AN ACCOUNTING SYSTEM INDEPENDENT OF POWER FAILURE; U.S. Pat. No. 4,285,050 for an ELECTRONIC POSTAGE METER OPERATING VOLTAGE VARIATION SENSING SYSTEM; U.S. Pat. No. 4,323,987 for a POWER FAILURE MEMORY SUPPORT SYSTEM; U.S. Pat. No. 4,445,198 for a MEMORY PROTECTION CIRCUIT FOR AN ELECTRONIC POSTAGE METER; U.S. Pat. No. 4,534,018 for a NON-VOLATILE MEMORY PROTECTION CIRCUIT WITH MICROPROCESSOR INTERACTION; and U.S. Pat. No. 4,484,307 for an ELECTRONIC POSTAGE METER HAVING IMPROVED SECURITY AND FAULT TOLERANCE FEATURES.
In addition to the foregoing patents, the assignee of the present invention is the assignee of other inventions concerning the aforesaid subject matter, which inventions are disclosed in U.S. patent application SN 542,225 of Arno Muller, filed Oct. 14, 1983, for a POSTAGE METER WITH POWER FAILURE RESISTANT MEMORY; U.S. patent application Ser. No. 643,111 of Kirschner et al, filed Aug. 22, 1984, for a DATA PROTECTION SYSTEM FOR ELECTRONIC POSTAGE METERS HAVING MULTIPLE NON-VOLATILE MEMORIES; U.S. patent application Ser. No. 643,111 of Kirschner et al, filed Aug. 22, 1984 for an ELECTRONIC POSTAGE METER HAVING MULTIPLE NON-VOLATILE MEMORIES FOR STORING DIFFERENT HISTORICAL INFORMATION REFLECTING POSTAGE TRANSITIONS; and U.S. patent application Ser. No. 643,219, filed Aug. 22, 1984 for a NON-VOLATILE MEMORY SYSTEM WITH READ TIME AND POWER DOWN DATA STORAGE CAPABILITY FOR AN ELECTRONIC POSTAGE METER.
Thus, the problem of protecting postage meter operating data upon the occurrence of a power failure condition may be said to have been voluminously addressed by the art. However, the problem persists. And applicant's present invention resides in the provision of yet another solution to a relatively long standing problem, when considered in the light of the pace of development of computer technology, of protecting the operating data stored in an electronic postage meter upon the occurrence of a power failure condition. Accordingly:
An object of the present invention is to provide, in a postage meter including computer means having means for storing postage meter operating data, an improvement for protecting the operating data; and
Another object is to provide in such a postage meter, wherein the computer means includes a microprocessor, means in the microprocessor for inhibiting the provision of a reset signal after power failure and until the operating data has been stored in a non-volatile memory.